Active isolation switch

Abstract

An active isolation switch according to this invention includes a field effect transistor (FET), a first bi-polar transistor and a second bi-polar transistor, and an emitter bias resistor. The FET is formed with a source, a gate, and a drain. The first bi-polar transistor is formed with a first emitter, a first base, and a first collector; the first emitter is connected to the source and the first collector is connected to the gate. The second bi-polar transistor is formed with a second emitter, a second base, and a second collector, the second base is connected to the first base, and the second collector is connected to the drain. The emitter bias resistor is formed with a first terminal and a second terminal; the first terminal is connected to the emitter of the second bi-polar transistor and the second terminal is connected to the emitter of the first bi-polar transistor. The first resistor is connected between a bias voltage and the first collector; the second resistor is connected between the bias voltage and the base of the second bi-polar transistor.

I claim: 
     
       1. An active isolation switch, comprising:
 a field effect transistor (FET), being formed with a source, a gate, and a drain, the source and the drain; for electrical connection and isolation between an output of the power supply (Input Terminal) and a bus (Output Terminal);
 a first bi-polar transistor, being formed with a first emitter, a first base, and a first collector, the first emitter being connected to the source and the first collector being connected to the gate; a second bi-polar transistor, being formed with a second emitter, 
 a second base, and a second collector, the second base being connected to the first base, and the second collector being connected to the drain; and 
 an emitter bias resistor, being formed with a first terminal and a second terminal, the first terminal being connected to the emitter of the second bi-polar transistor and the second terminal being connected to the emitter of the first bi-polar transistor. 
 
 
     
     
       2. The active isolation switch according to  claim 1 , wherein the first collector and the second base connected to the first bias current and second bias current respectively. 
     
     
       3. The active isolation switch according to  claim 2 , wherein the first bias current is drawn from the bias voltage coupled to the first resistor and the second bias current is drawn from the bias voltage coupled to the second resistor. 
     
     
       4. The active isolation switch according to  claim 3 , wherein the first bi-polar transistor and the second bi-polar transistor are matched-pair transistors packaged in one. 
     
     
       5. The active isolation switch according to  claim 2 , wherein the first bi-polar transistor and the second bi-polar transistor are matched-pair transistors packaged in one. 
     
     
       6. The active isolation switch according to  claim 1 , wherein the first bi-polar transistor and the second bi-polar transistor are matched-pair transistors packaged in one.